The present invention generally relates to the field of mineral ore processing, and more particularly, to a mixing apparatus and to uses thereof in the separation of minerals from mineral-bearing ores.
Processes are known in the prior art which provide for the separation of minerals from mineral-bearing ores.
For example, in known processes used for the separation of copper from copper-bearing ores, illustrated diagrammatically in FIG. 1, non-oxidized ores 20 (which might contain as little as 0.5% copper, and typically contain iron sulfides) are processed in a crusher 22, with water 24, to form a slurry 26. The slurry 26 is then transferred to a flotation cell 28, and subjected to physical action, specifically, air sparging and mixing. As a result of the physical action, a substantial portion of the copper value in the slurry 26 rises to the surface of the flotation cell 28 as a froth 30, and is skimmed therefrom by a paddle mechanism 32, while the waste rock 33 (xe2x80x9cganguexe2x80x9d) remains in the bulk, and is ultimately passed from the cell 28 to a dryer 34 and discharged as tailings 36. This process of xe2x80x9cfroth separationxe2x80x9d results from differences in wettability of copper as compared to other minerals, and is typically aided by chemical frothing and collector agents 38 added to the slurry 26, such that the froth 30 from such flotation contains 27 to 36% copper. Methylisobutyl carbonal (MIBC) is a typical frothing agent, and sodium xanthate, fuel oil, and VS M8 (a proprietary formulation) are typical collector agents.
The froth 30 is then fed to an oxygen smelter 40, and the copper and iron sulfides are oxidized at high temperature resulting in impure molten metal 42 (97-99%, copper, with significant amounts of iron oxide) and gaseous sulfur dioxide 44. The impure metal 42 is then transferred to an electrolytic purification unit 46, which separates the impure metal 42 into 99.99% purity copper material 48 and slag 50.
The gaseous sulfur dioxide 44 is collected in a reactor 52 wherein it is scrubber and mixed with water 24 to form sulphuric acid 54. The sulphuric acid 54 is suitably blended with water 24 and used to leach oxidized ores, typically by xe2x80x9cheap leachingxe2x80x9d an ore pile 56. The resultant copper-bearing acid 58 is known as xe2x80x9cpregnant leach solutionxe2x80x9d. Pregnant leach solution 58 is also obtained by mixing solutions of sulphuric acid 54, in vats 60, with the tailings 36 discharged from flotation operations, to dissolve the trace amounts of copper remaining therein.
The copper is xe2x80x9cextractedxe2x80x9d from the pregnant leachate 58 by mixing therewith, in a primary extraction step 62, organic solvent 64 (often kerosene) in which copper metal preferentially dissolves. Organic chemical chelators 66, which bind solubilized copper but not impurity metals, such as iron, are also often provided with the organic solvent, to further drive the migration of copper. Hydroxyoximes are exemplary in this regard.
In the primary extraction step 62, the copper is preferentially extracted into the organic phase according to the formula:
[CuSO4]aqueous+[2 HR]organicxe2x86x92[CuR2]organic+[H2SO4]aqueous 
where HR=copper extractant (chelator)
The mixed phases are permitted to separate, into a copper-laden organic solvent 68 and a depleted leachate 70.
The depleted leachate 70 is then contacted with additional organic solvent 72 in a secondary extraction step 74, in the manner previously discussed, and allowed to settle, whereupon the phases separate into a lightly-loaded organic (which is recycled as solvent 64 in the primary extraction step) and a barren leachate or raffinate 76.
The barren leachate 76 is delivered to a coalescer 78 to remove therefrom entrained organics 80, which are recycled into the system; the thus-conditioned leachate 82 is then suitable for recycling into the leaching system.
The pregnant organic mixture 68 (produced in the primary extraction step 62) is stripped of its copper in a stripping operation 84 by the addition of an aqueous stripping solution of higher acidity 86 (to reverse the previous equation); after phase separation, a loaded electrolytic solution 88 (xe2x80x9crich electrolytexe2x80x9d) remains, as well as an organic solvent, the latter being recycled as solvent 72 in the secondary extraction 74.
The rich electrolyte 88 is directed to an electrowinning unit 90. Electrowinning consists of the plating of solubilized copper onto the cathode and the evolution of oxygen at the anode. The chemical reactions involved with these processes are shown below
Cathode: CuSO4+2 e1xe2x88x92xe2x86x92Cu+SO42xe2x88x92
Anode: H2Oxe2x86x922H++0.5 O2+2 e1xe2x88x92
This process results in copper metal 92, and a lean (copper-poor) electrolyte, which is recycled as stripping solution 86.
The combination of leaching, combined with extraction and electrowinning, is commonly known in the art as solvent extraction electrowinning, hereinafter referred to in this specification and in the claims as xe2x80x9cSXEWxe2x80x9d.
In a known application of the described SXEW process, in both the primary 62 and secondary 74 extraction steps, the combined organic and aqueous phases are delivered through a series of mixing vessels (primary P, second S and tertiary T), and then to a settling tank ST, the primary mixing vessel P being about 8 feet in diameter and 12 feet in height, and stirred by a rotary mixer driven by a 20 horsepower motor, and each of the secondary S and tertiary T mixing vessels being about 12 feet in diameter and height, and stirred by a rotary mixer driven by a 7.5 horsepower motor. (The system of primary P, secondary S and tertiary T mixers, and settling tank ST, is replicated to meet volume flow requirements, with each system processing about 10,000 gpm). This provides a mixing regime wherein the organic and aqueous phases are intimately mixed for a period of time sufficient to allow copper exchange (to maximize copper recovery), yet relatively quickly separate substantially into organic and aqueous phases.
In a known application of the froth flotation process, a plurality of flotation cells 28, each being approximately 5 feet square and 4 feet high, are utilized, with pairs of cells sharing a 50 horsepower motor driving respecting rotary mixers (not shown). This provides a mixing regime sufficient to allow the air bubbles to carry the copper value to the surface.
Various modifications can be made to the rotary mixers in the extractors and in the flotation tanks of the foregoing process. However, the general configurations noted above have been found to provide relatively economical results, and significant variations therefrom can impact adversely upon economies. For example, an attempt to reduce energy costs by scaling-down the motors for the mixers would have consequent impacts either upon the copper recovery efficiency, or upon available process throughputs. Specifically, the relatively large motors employed are required to drive the sturdy (and therefore heavy) rotary mixers and shafts that are needed to withstand the torques caused by rotation; lower power motors would demand either lower blade speed or smaller blades, with consequent impacts upon mixing and transfer efficiency.
It is an object of the present invention to provide a novel mixing apparatus.
This object is met by the present invention which comprises a mixing apparatus. The mixing apparatus is advantageously used with a vessel having a contiguous sidewall centered about and defining a longitudinal axis.
As one aspect of the present invention, the mixing apparatus comprises a mixing head having a tubular blade portion centered about and defining a head axis and having a first tube end and a second tube end spaced-apart from one another therealong.
The blade portion tapers from the first tube end to the second tube end with the inner surface of the blade portion and the second end defining an inside blade diameter xe2x80x9cIDxe2x80x9d and the outer surface of the blade portion and the first end defining an outer blade diameter xe2x80x9cODxe2x80x9d. The mixing apparatus further comprises mounting means for mounting the mixing head substantially coaxial to and within the vessel for longitudinal movement relative thereto. Also provided is a reciprocating means for effecting said longitudinal relative movement of the mixing head in a reciprocating manner through a stroke length xe2x80x9cSxe2x80x9d, with a duration xe2x80x9cTxe2x80x9d for each cycle, wherein 175xe2x89xa60.36xc3x97OD2/ID2xc3x97S/Txe2x89xa6250 when OD, ID and S are each expressed in inches, and T is expressed in minutes.
As other aspects of the invention, the blade portion preferably tapers in a substantially frustoconical manner from the first tube end to the second tube end, and an angle xcex1, defined by the angle between the pair of axes defined by and coincident with the intersections of the outer surface of the blade portion and a plane coincident with the head axis, preferably lies between 90xc2x0 and 180xc2x0.
As other aspects of the present invention, the mounting means preferably comprises a mixer shaft. The mixer shaft has a bottom end operatively rigidly connected to the mixing head by a hub member rigidly connected to the bottom end of the mixer shaft and a plurality of support webs extending between and connecting the hub member and the blade portion, and extends from said bottom end, substantially parallel to the head axis, to a top end which is disposed above the vessel in use.
As yet another aspect of the present invention, the reciprocating means preferably comprises shaft gripping means for gripping the mixer shaft adjacent the top end thereof and effects longitudinal reciprocating movement of the shaft gripping means through stroke length xe2x80x9cSxe2x80x9d with duration xe2x80x9cTxe2x80x9d for each cycle, thereby to effect longitudinal movement of the mixing head in said reciprocating manner.
As another aspect of the present invention, a housing, positionable above said vessel, is preferably provided, and the reciprocating means preferably comprises a flywheel, a crank member, and a yoke.
The flywheel is mounted to the housing for rotation about a rotational axis which is normal to the longitudinal axis.
The crank member projects from the flywheel in a direction parallel to the rotational axis and is connected to the flywheel for rotation therewith.
The yoke is displaced from the flywheel in the direction of the crank member and has a substantially linear race formed therein which is in receipt of the crank member and is adapted to permit relative translational movement of the crank member and the yoke.
The yoke is positioned with the race arranged normal to the rotation axis and bisected thereby and is mounted to the housing in a manner which constrains movement of the yoke otherwise than along an axis parallel to the longitudinal axis and normal to the rotational axis, such that during rotation of the flywheel, the crank member imparts longitudinal reciprocating movement to the yoke.
As yet another aspect of the invention, the shaft gripping means is preferably operatively rigidly connected to the yoke for longitudinal reciprocating movement therewith.
As another aspect of the present invention, the mounting means is preferably adapted to mount the mixing head within the vessel with the first tube end disposed above the second tube end.
The invention also comprises use of the mixing apparatus as a mixer for a vessel in an SXEW extractor unit, and as a mixer for the vessel in a froth flotation cell.
Other advantages, features and characteristics of the present invention, as well as methods of operation and functions of the related elements of the structure, and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following detailed description and the appended claims with reference to the accompanying drawings, the latter of which is briefly described hereinbelow.